It is well known in the prior art to form thermally insulating doors or fire-resistant doors. In U.S. Pat. No. 2,924,860, there is disclosed a thermally insulating door comprising a block of expanded polystyrene provided with cover sheets of relatively thin, strong hard material such as fiber glass laminated by polyester resin to mahogany plywood. The patent states that additional strength may be provided by employing a lamination including a hard board such as wood, plywood, metal or the like between the fiber glass and the foamed or expanded plastic slab or block.
In U.S. Pat. No. 3,225,505, there is disclosed a door having a continuous expansion joint between a substantially fireproof core and a fire-resistant frame. The core is produced from expanded mineral particles which, with the aid of mineral fibers and a mineral binder, are united inseparably together to form a unitary rectangular panel. The door may be made of smaller pieces if they are formed along their meeting edges with a tongue and groove joint. The outer skins have adhesive applied to the inner sides thereof and the fireproof core. The adhesive is a thermo-setting adhesive with a cold press time for bonding the skins to the core and the frame. The adhesive applied is applied by a power glue spreader.
There are a number of problems with the prior art doors. In the latter case, U.S. Pat. No. 3,225,505 requires the outer skin to be formed of three plies that are permanently bonded together into a unitary structure. When the plywood skins are positioned upon opposite faces of the core and frame of the door, a suitable adhesive spread is applied thereto and to the inner faces of the skins. The adhesive is a thermo-setting adhesive having a working life of 24 hours, an assembly time of 15 to 20 minutes, and a cold press time of 24 minutes. The glue or adhesive is applied by a power glue spreader. There is a great deal of cost in making such doors because of the construction of the three plies forming the outer skin permanently bonded together, the preparation of the core and the application of glue to both the core and the outer skins and using a cold press to bond the skins to the core.
In U.S. Pat. No. 2,924,860, the core material is polystyrene but the outer layer is fiber glass laminated to another layer such as mahogany plywood, asbestos, cement board, metal, fiber board, or plastic materials. Hardware is attached to the outside thereof with screws immersed in screw holes filled with flowable plastic material that hardens around the screw to hold the screw in the polystyrene.
The present invention overcomes the disadvantages of the prior art by providing a door which is light in weight, is environmentally safe because of the components used and the manner of manufacture, acts as an insulator, and is durable. The door formed could be a door applicable to buildings generally for ingress and egress, or may form a garage door by coupling several door panels together. For purposes of simplicity, the present case will be discussed in terms of a garage door although, as stated earlier, it is equally applicable to other doors for ingress and egress.
In the present invention, a steel skin for the front of the door or door panel is embossed and textured with a predetermined pattern. A polystyrene panel is molded having the same predetermined pattern on one side thereof and a relatively smooth textured surface on the other side. A substantially flush textured steel back skin is formed. The embossed steel is preheated to a temperature necessary to receive a pressure sensitive hot melt adhesive on the back side thereof without actually cooling the adhesive by conducting the heat away from the hot adhesive to the cold steel. The pressure sensitive hot melt adhesive is sprayed on the back side of the embossed skin and the molded polystyrene panel having the corresponding pattern as the embossed steel is mated with the steel front skin to form a first assembly. The front embossed skin is, as stated previously, preheated to the point that it does not substantially conduct the heat from the hot melt adhesive until the bonding can take place between the steel and the polystyrene core. The pressure sensitive hot melt adhesive is also applied to the inside of the steel back skin and then the back skin is mated to the smooth side of the molded polystyrene panel in the first assembly to form a second assembly having the front and back steel skins with the molded panel as a core. Hot melt adhesive is applied on the inside of the end caps and then they are mated with the ends of the second assembly. The second assembly is then heated to a temperature sufficient to keep the hot melt adhesive soft and tacky and, while at that temperature, pressure is applied in the range of 15 to 25 pounds per square inch to the second assembly by a series of rollers to create the adhesive bonds between the front and back steel skins and the polystyrene core. Metal end caps are formed to cover the exposed polystyrene ends.
By this method, a door or door panel is constructed that is lightweight, environmentally safe, insulating and durable.
When a plurality of the door panels are attached together by hinges, a garage door results.